Trunking communication technologies are characterized by special features such as scheduling, group calling, and fast calls and, therefore, are widely used in the field of specialized communications.
A trunking group call service, which is a most fundamental service provided in the trunking communication technology, allows a user equipment to establish a group call to a group of user equipments in a given area, where the given area is referred to as a trunking group call area. In a process of implementing the trunking group call service, members with two types of identities are involved, namely, a scheduler and a user equipment that has subscribed to the trunking group call service. There may be no scheduler in a group. All user equipments in the group, except the scheduler, perform communication in a half-duplex manner. During a call, only one user equipment (a user equipment in a group-sending state) in the group talks at a time, and other user equipments (user equipments in a group receive state) listens passively. Each user equipment in the group may preempt a floor by pressing a PTT button (push to talk: push to talk) and get an opportunity to talk; other user equipments in the group can get the floor only after the user equipment that is granted the floor to talk releases the PTT button.
Each group has one unique group identification for implementing the trunking group call service. Any user equipment in the group may initiate a group call to the group. A user equipment in the group may initiate a group call of the group by inputting the group identification of the group and then pressing the PTT button, thereby implementing the trunking group call service. When the trunking group call service is implemented in a GSM network, two specific operating states are available:
a group receive state: a user equipment operates as a receiver of trunking group call service data, where a cell allocates no dedicated channel to the user equipment and the user equipment can only listen to group call information; and
a group transmit state: the user equipment operates as a sender of the trunking group call service data, where the cell allocates, to the user equipment, two dedicated uplink channels, which are used to separately transmit data information and control information sent by the user equipment.
The development of an LTE system has resulted in a user requirement for implementing trunking communication in the LTE system, for example, implementing a trunking group call service in the LTE system. However, the LTE system has only a packet switched domain, where packet data is scheduled and transmitted by using a shared channel; therefore, in the LTE system, an evolved cell cannot allocate a dedicated channel for the trunking group call service. As a result, how to implement the trunking group call service in the LTE system becomes an important topic.